Deep Excavation Analysis Supported by Anchored Diaphragm Walls: A comparison of Constitutive Models

This paper presents a numerical study of a large and deep excavation in clay soil supported by anchored diaphragm walls under unequal load to investigate the influence of several design parameters on the stability and safety of the supporting system and their impacts on the surrounding nearby structures using the Plaxis 2D v20 code. The numerical model result was compared with a case study of braced excavation in the clays, and a close match between the results was observed. The soil profile consists of several clay layers and is modeled with two constitutive modes: the Mohr-Coulomb model (MCM) and the hardening soil with a small strain model (HSsmall). The diaphragm walls were modeled as plates and the anchor rods as node-to-node connections. The studied parameters include the inclination angle of anchors, number of ground anchors, surface load magnitude, various ratios of wall-embedded depth to the excavation depth on a deep excavation, and the heave developed at the bottom of the excavation. It was observed that as  is increased from 0.3 to 0.5,  and  is reduced by approximately 6.7% and 14.7%, respectively, for the MCM, compared to 10.5% and 8.1% by the HSsmall modeling. Whereas  increased to 0.7, the values of  and  in both models remained unchanged. Furthermore, for all studied ratios, the MCM produces around 28 mm of heave compared to 23 mm for the HSsmall model. In general, the outcome results of the analysis were examined and discussed in terms of maximum values of lateral displacements, bending moments in the wall supporting system, and the settlement of the ground surface behind both sides of the excavation, which can serve as a reference for deep excavation design and similar geotechnical problems.